1. Field of the Invention
The present invention relates to an audio packet communications system that comprises a LAN (Local Area Network), a plurality of telephone terminals connected to the LAN, and a telephone network such as the public network and a dedicated network. In the system, audio packets are transmitted between the network telephone terminals and between any network telephone terminal and the telephone network.
2. Description of the Related Art
Conventional private network systems comprise a PBX (Private Branch Exchange) or a host apparatus and audio communications terminals such as telephones. The audio communications terminals are connected to the PBX or the host apparatus and function as extension terminals. The PBX or the host apparatus connects any extension terminal to the external communications network such as the public network or a dedicate communications network. Therefore, the extension terminals can communicate with one another, and each extension terminal can communicate with any terminal provided on the public network or dedicated communications network, via the PBX or the host apparatus. Data terminals, such as personal computers, are connected to the LAN. The data terminals can therefore exchange E-mails and data with one another through the LAN. A communications system has been proposed, which comprises an audio communications system having a PBX or a host apparatus, a data communications system having a LAN, and a gateway that links the audio communication system and the data communications system.
A system has been proposed in recent years. This system comprises audio communications terminals (e.g., telephones), a LAN that connects these terminals, and a host apparatus that connects the LAN to an external communications network such as the public network or a dedicated network. In the system, the audio communications terminals can communicate with one another, and each audio communications terminal can communicate with any audio communication terminal provided on the external communications network. Each audio communications terminals and the host apparatus perform convert protocol and data format.
When any audio terminal performs a holding process in the system described above, the host apparatus issues a holding tone. The holding tone is transmitted, in the form of a packet, to not only the audio terminal but also the terminal with which the audio terminal is communicating.
In the system described above, two or more audio terminals may assume the holding state at the same time. If this happens, the LAN band needs to be broad in proportion to the number of audio terminals in the holding state. The communications traffic on the LAN inevitably increases. In some cases, the communication traffic may surpass the traffic capacity of the LAN. Such a heavy traffic may greatly delay the transmission of data and other calls in the LAN, or may result in a loss of some packets in the LAN.
To prevent these troubles in the LAN, a system has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 2000-59471. In this system, the telephone terminals connected to a LAN have a holding-tone source each. The use of a holding-tone source for each telephone terminal not only renders the system large and massive, but also increases investment cost on the part of the users.